In Planta Localization of Endophytic Cordyceps fumosorosea in Carrizo Citrus

Entomopathogenic fungi can be a useful resource for controlling insect vectors of citrus plant pathogens, such as the Asian citrus psyllid (Diaphorina citri) associated with huanglongbing or the citrus root weevil (Diaprepes abbreviatus) associated with the spread of Phytophtora spp. In this study, Cordyceps fumosorosea (Cfr) was investigated in planta as a potential endophytic entomopathogenic fungus and various inoculation techniques were used to determine if it would colonize the Carrizo citrange (Citrus × insitorum) seeds and plants. The four inoculation methodologies evaluated were seed soaking, stem injection, foliar spray, and soil drench. Seed immersion trials demonstrated that the roots of the Carrizo citrange plant can be inoculated successfully with Cfr. Stem injection, foliar spray, and soil drench also provided successful inoculation of Cfr. However, this fungus was only endophytic in the plant stem. Sand cores indicated that Cfr moved down through the sand column and was able to inoculate the roots. Given the prevalence of Cfr in the soil during the drench experiment, and that the fungus was able to colonize Carrizo citrange roots through seed immersion, this finding provides evidence of the potential endophytism of this fungus when applied to citrus plant species.

Drought Stress Impairs Communication Between Solanum tuberosum (Solanales: Solanaceae) and Subterranean Biological Control Agents

The attraction of entomopathogenic nematodes (EPNs) to herbivore-injured plant roots has been documented recently to be a common tritrophic interaction. Belowground tritrophic interactions are especially subject to modulation by many abiotic factors including drought. In this study, complementary greenhouse experiments were conducted to understand how drought stress might affect a potato plant’s impact on EPN behavior. In separate trials, the responses of the EPN Steinernema diaprepesi (Nguyen and Duncan) (Rhabditida: Steinernematidae) to root herbivory by larvae of the weevil Diaprepes abbreviatus (Linnaeus) (Coleoptera: Curculionidae), in well-watered and drought stressed potato plants, were measured using soil-matrix olfactometers with two arms. The drought treatments were initiated in 30-d old plants. Drought-stressed potato plants received water when potentiometers read approximately 20 kPa, while for well-watered plants, the number was 8 kPa. Four weeks after initiating the treatments, 400 ml water was added to all pots, immediately before starting the experiments. The experiments revealed that S. diaprepesi infective juveniles (IJs) did not migrate preferentially toward drought-stressed or well-watered plants when neither were subjected to herbivory [t(21) = 1.13, P = 0.269]. However, plants with roots damaged by herbivory attracted more S. diaprepesi IJs if they were well watered than if they were drought stressed [t(24) = 3.19, P = 0.004]. If both plants in the olfactometers were drought stressed, EPNs moved preferentially toward those with root herbivory than those with undamaged roots [t(23) = 3.19, P = 0.004]. No difference was detected in gas chromatography profiles between droughted and well-watered plant roots subjected to herbivory [F(24, 336) = 0.68, P = 0.87]. GC analysis showed that three compounds, including 3-nonanone [t(6) = 4.83, P = 0.003], artemisyl ketone [t(7) = 6.21, P = 0.000], and benzoic acid, 4-ethoxy-, ethyl ester [t(7) = −4.22, P = 0.004] were significantly higher in drought stressed than control plant roots. These results indicate that potatoes, like other plants, can recruit EPNs in response to root herbivory, and that drought stress dampens this tritrophic interaction where choice is involved. Additional research that resolves the mechanisms of these interactions may provide insights to exploit EPNs for crop protection.

Field Diagnosis of Citrus Root Weevil Damage

Root weevils infest citrus groves throughout the citrus growing regions of Florida. Among the eight weevil species that have been identified in Florida citrus groves, five have some potential to cause economic problems for nurserymen and commercial growers. The most important weevil species are Diaprepes root weevil (Diaprepes abbreviatus), southern blue-green citrus root weevil (Pachnaeus litus), and the blue-green citrus root weevil (Pachnaeus opalus). The little leaf notcher (Artipus floridanus) and Fuller rose beetle (Asynonychus godmani) are of less concern, but may be locally important (Fig. 1). This paper will deal with Diaprepes and the blue-green root weevils because they are of major economic importance and frequently occur in citrus groves. This document is HS-1014, one of a series of the Horticultural Sciences Department, UF/IFAS Extension. Original publication date May 2005. HS-1014/HS260: Field Diagnosis of Citrus Root Weevil Damage (ufl.edu)

Diaprepes Root Weevil on Southern Highbush Blueberry in Florida

Citrus root weevil, Diaprepes abbreviatus (Linnaeus) is a destructive pest on citrus trees. It is now becoming a significant pest on blueberry in central Florida, at times causing major damage to blueberry bushes that are more than two years old. This 3-page fact sheet written by Douglas A. Phillips, Oscar E. Liburd, and Larry W. Duncan and published by the UF/IFAS Entomology and Nematology Department will educate blueberry growers on how to monitor, identify, and control citrus root weevil. http://edis.ifas.ufl.edu/in1241